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Summary

Physical Characteristics

Juglans_nigra is a deciduous Tree growing to 30 m (98ft) by 20 m (65ft) at a fast rate. It is hardy to zone (UK) 4 and is not frost tender. It is in flower from May to June, and the seeds ripen in October. The species is monoecious (individual flowers are either male or female, but both sexes can be found on the same plant) and is pollinated by Wind. The plant is self-fertile. Suitable for: light (sandy), medium (loamy) and heavy (clay) soils and prefers well-drained soil. Suitable pH: acid, neutral and basic (alkaline) soils. It cannot grow in the shade. It prefers moist soil.

Synonyms

Habitats

Edible Uses

Seed - raw or cooked. A sweet, rich distinctive delicious flavour it makes an excellent dessert nut and is also widely used in confections, cakes etc[2, 34, 82, 183]. The kernel is hard to extract and the oil it contains quickly turns rancid[101, 159]. The unripe fruits can be pickled[183]. The seed is borne in solitary fruits or in pairs and is 3 - 4cm in diameter[82, 229]. The nuts can leave a permanent stain on clothing[226]. An edible oil is obtained from the seed[101, 183]. A sweet taste but it tends to go rancid quickly[159]. Used as a seasoning in bread, squash and other foods[183]. The tree yields a sweet sap that can be drunk or concentrated into syrup or sugar[101, 102, 183]. It is tapped in spring.

Medicinal Uses

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The bark and leaves are alterative, anodyne, astringent, blood tonic, detergent, emetic, laxative, pectoral and vermifuge[4, 222, 257]. Especially useful in the treatment of skin diseases, black walnut is of the highest value in curing scrofulous diseases, herpes, eczema etc[4]. An infusion of the bark is used to treat diarrhoea and also to stop the production of milk, though a strong infusion can be emetic[21, 257]. The bark is chewed to allay the pain of toothache and it is also used as a poultice to reduce the pain of headaches[222, 257]. The juice from the fruit husk is applied externally as a treatment for ringworm[222, 257]. The husk is chewed in the treatment of colic and applied as a poultice to inflammations[222]. The burnt kernels, taken in red wine, are said to prevent falling hair, making it fair[269]. Green husks are supposed to ease the pain of toothache[269]. A tea made from the leaves is astringent[222]. An infusion has been used to lower high blood pressure[257]. It can be used as a cleansing wash[21]. The pulverized leaves have been rubbed on the affected parts of the body to destroy ringworm[257]. The oil from the ripe seeds has been used externally in the treatment of gangrene, leprosy, and wounds[269]. The sap has been used to treat inflammations[257].

Other Uses

A brown dye is obtained from the nuts, husks and bark[14, 57, 101, 159]. It does not require a mordant[169]. The husks can be dried for later use[169]. A brown dye is obtained from the leaves and stems[168]. It does not require a mordant[168]. The dye turns black if it is prepared in an iron pot[168]. The leaves can be dried for later use[169]. The husks are rich in tannin[226]. The green fruit husks can be boiled to provide a yellow dye[269]. The husks can be made into a high quality coal (does the report mean charcoal?[K]) and is then used as a filter[226]. It was used in gas masks[226]. The woody shells on the fruits have been used to make jewellery[269]. Insects are said to avoid the walnut tree, hence it is often used as a poor man's insect repellent. When rubbed on faces, walnut leaves are said to repel flies[269]. The leaves repel fleas and have been used as a strewing herb[20, 201, 257]. They are also used as an insecticide against bed bugs[222]. The ground up husks are also insecticidal[226]. The leaves produce substances that depress the growth of other plants. These substances are washed onto the ground by rain and inhibit the growth of plants beneath the tree[18, 20, 159]. The roots also produce substances that are toxic to many plant species, especially apples (Malus species), members of the Ericaceae, Potentilla spp and the white pines (certain Pinus spp.)[200]. An alternative ingredient of 'QR' herbal compost activator[32]. This is a dried and powdered mixture of several herbs that can be added to a compost heap in order to speed up bacterial activity and thus shorten the time needed to make the compost[K]. Wood - very ornamental, heavy, hard, strong, close-grained, very durable. Easily worked, it glues well, does not warp, shrink or swell much and takes a good polish. It weighs 38lb per cubic foot. A very valuable timber tree and possibly the most sought after wood in N. America, it is used in cabinet making, the interior finishes of houses, furniture, airplanes, ship building, veneer etc[1, 46, 61, 82, 101, 149, 227, 229, 235, 269].

Cultivation details

Landscape Uses:Firewood, Aggressive surface roots possible, Specimen. Requires a deep well-drained loam and a sunny position sheltered from strong winds[1, 11]. Prefers a slightly alkaline soil[200]. Plants are best suited to deep, rich, slightly acid or neutral soil, with good drainage, but will not succeed on infertile upland soil or on soils with poor drainage[269]. The black walnut grows best areas with an annual precipitation from 30 to 130cm, an annual temperature in the range of 7 to 19°C and a pH from 4.9 - 8.2[269]. The dormant plant is very cold hardy, but the young growth in spring, however, can be damaged by late frosts. The Black walnut is one of most valuable natural forest trees in the United States[269]. A very ornamental and fast growing plant[1, 200], it is sometimes cultivated in N. America for its edible seed. Whilst potential yields of 7.5 tonnes per hectare have been postulated, it is more feasible to expect annual yields of around 2.5 tonnes per hectare[269]. Good seed crops are usually produced every other year, though some plants fruit well annually whilst others produce god crops every third year[269]. The average weight of a seed from wild trees is about 17g, though there are many named varieties and the weight of their seeds varies from 20 - 30g[183, 269]. There are breeding programmes that are seeking to develop cultivars with thinner shells[226]. Trees in the wild commence bearing seeds when about 12 years old[227]. Black walnut trees mature their fruit rather generally throughout the plants natural range where there is a growing season of about 150 days and an average summer temperature of 16.5°C[269]. Trees do not fruit very freely in Britain unfortunately[1, 11]. They grow well in the eastern half of the country but often do not thrive in the west[98]. Trees have been extensively planted for timber in parts of C. and E. Europe[50]. This species hybridizes with J. regia[149], some named cultivars have been developed from this cross for their seed. Plants produce a deep taproot which makes them very drought resistant when established, though they are intolerant of root disturbance[1, 11, 269]. Seedlings should be planted out into their permanent positions as soon as possible and given some protection for their first winter or two since they are somewhat tender when young[1, 11]. Flower initiation depends upon suitable conditions in the previous summer[200]. The flowers and young growths can be destroyed by even short periods down to -2°c, but fortunately plants are usually late coming into leaf[200]. The black walnut is self-fertile, but the sequence of male and female blooming, called dichogamy, can and often does minimize chances of a tree shedding pollen on its own pistils. In different trees pollen may be shed before the receptivity period of female flowers, or at same time, or after pistil receptivity. For greatest possible nut production, plant trees of 2 or more cvs, as different cvs have overlapping pollen-receptivity periods and can pollinate each other[269]. Any pruning should only be carried out in late summer to early autumn or when the plant is fully dormant otherwise wounds will bleed profusely and this will severely weaken the tree[200]. Plants produce chemicals which can inhibit the growth of other plants. These chemicals are dissolved out of the leaves when it rains and are washed down to the ground below, reducing the growth of plants under the tree[18, 20, 159]. The roots also produce substances that are toxic to many plant species, especially apples (Malus species), members of the Ericaceae, Potentilla spp and the white pines (certain Pinus spp.)[200]. Beans, peas and tomatoes are also particularly sensitive to these secretions and will not grow in the rooting zone[200]. Trees cast quite a dense shade so, along with their other anti-social tendencies, are not very friendly trees for a woodland garden[K]. The bruised leaves have a pleasant sweet though resinous smell[245]. Special Features:
Attracts birds, North American native, Inconspicuous flowers or blooms.

The PFAF Bookshop

Plants For A Future have a number of books available in paperback and digital form. Book titles include Edible Plants, Edible Perennials, Edible Trees, and Woodland Gardening. Our new book to be released soon is Edible Shrubs.

Propagation

The seed is best sown as soon as it is ripe in individual deep pots in a cold frame[80]. You need to protect it from mice, birds, squirrels etc. The seed usually germinates in late winter or the spring. Plant out the seedlings into their permanent positions in early summer and give some protection from the cold for their first winter or two. The seed can also be stored in cool moist conditions (such s the salad compartment of a fridge) over the winter and sown in early spring but it may then require a period of cold stratification before it will germinate[78, 80, 113].

Other Names

If available other names are mentioned here

Found In

Countries where the plant has been found are listed here if the information is available

Weed Potential

Right plant wrong place. We are currently updating this section.
Please note that a plant may be invasive in one area but may not in your area so it’s worth checking.

Expert comment

Author

Botanical References

Links / References

Readers comment

Thu Oct 16 03:41:59 2003

"Black Walnut

Juglans nigra

Black Walnut is one of the most well-known, valuable and largest native hardwoods in North America, widely distributed in the eastern states and extending northward to Canada. The Black Walnut trees grow over 100 feet tall with trunks measuring 3 feet in diameter. They thrive in mixed forests on moist soil with good drainage, commonly found in valleys.

The Black Walnut is covered with a green pulp coating while on the tree, which turns black when it falls on the ground or kept in storage.

In Russia the Black Walnut is known by the common name of Greek Nut (Juglan regia), which grows in Kaukaz and Middle Asia. Russian folk medicine came to rely on the Black Walnut for various botanical treatments.

In India and Pakistan, the Black Walnut is known as Akhort or Akshot, with similar uses in traditional Indian and Pakistani folk medicine."

How do you decrease the walnut production. Mess Mess Mess in yard.
dnally@bellsouth.com

Pete Vander Plaats; Orange City, Iowa

Sat Aug 26 2006

In 2006, we experienced a long period without rain. When it did rain the
rest of our lawn greened up quickly, however the portion of lawn which
was under the canopy of three large bllack walnut trees has failed to
green up. Is this due to the tannin which has been put down in this
area over the years?

Sun Dec 17 2006

These nuts are really good for dye

tatiana

Sun Dec 17 2006

what animals live in thetree juglans nigra?

Lorax

Sun Jun 8 2008

Walnuts can also be preserved in maple syrup to produce the tasty Southern dish called Wet Nuts.
Here in Ecuador we have the variety J. neotropica which has identical uses to standard black and Persian walnuts.

Feb 20 2012 12:00AM

Will Juglans nigra cross pollinate with English walnut to increase nut production? In order for this to be effective, how close must the trees be together? If there is a house in between them, will there be significantly less cross-pollination? Thank you. Thank you, PFAF for your great info.

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